Blade or vane for a gas turbine engine

ABSTRACT

The invention relates to a blade or vane for a gas turbine engine which comprises a carbon fibre reinforced matrix material which is further strengthened by strong ductile metal wires whose modulus of elasticity is similar to that of the carbon fibres.

Unlted States Patent 11 1 1111 3,756,746 Baker Sept. 4, 1973 [54] BLADE OR VANE FOR A GAS TURBINE 2,919,889 1/1960 Rube] 4I6/24l ux ENGINE 3,371,407 3 1968 Forsyth CI. al. 416/230 ux 3,403,844 10/1968 Stoffer 416 230 Inventor: Alan Anthony Baker, Bramcote, 3,616,508 11 1971 Wallett 416/230 x England FOREIGN PATENTS OR APPLICATIONS [73] Assgnee: g' g fz f t: f z f [Mensa "l 596,636 1/1948 Great Britain 416 230 P Y s ovemme 619,634 3/1949 Great Britain 416 230 a i 3 8 3"" 787,500 12 1957 Great Britain 416 230 l'l am an 0| ern re an Whitehall, London, England 1 OTHER PUBLICATIONS [22] Filed: Sept. 13, 1971 AFC. Applzigcation3of Bitterli et al., No. 318,662, Pubish d Ju 194 21 Appl. No.: 180,049 6 Primary ExaminerEverette A. Powell, Jr. [30] Foreign Application Priority Data Attorney-Cushman, Darby & Cushman Sept. 15, 1970 Great Britain 43,924 70 57 ABSTRACT [52] US. Cl. 416/230, 416/241 51 Int. Cl. F0ld 5/14 h Invention {dates to blade or vane for [58] Field 6: Search 416/230, 229, 241 A bme engme which compflses a carbon fibre remforced matrix material which is further strengthened by strong 5 References Cited ductile metal wires whose modulus of elasticity is simi- UNTED STATES PATENTS lar to that of the carbon fibres. 2,868,439 l/l959 Hampshire et al 4161220 UX l0 Claims, 4 Drawing Figures 1 BLADE OR VANE FOR A GAS TURBINE ENGINE vere overloads without breaking off and consequently further damaging the engine.

The present invention provides a blade or vane which can be arranged to withstand considerable overload without breaking off.

According to the present invention a blade or vane for a gas turbine engine comprises a carbon fibre reinforced matrix material and a further reinforcement of piano wires or other strong ductile metal wires with a comparative modulus embedded within the matrix and extending longitudinally the blade.

The fraction of the blade made up of the wire reinforcement will vary according to the specific requirements to be met, but we prefer to use some percent by volume of the wire to keep the blade density as low as possible. I

The wires need not be evenly dispersed throughout the cross section of the blade, nor need they extend over the full length of the blade. Thus the reinforcement may be concentrated near the blade surface or near the leading and trailing edges of the blade, and may extend from the blade root over only the inner major part of the blades longitudinal extent.

The wires need not be of a similar diameter to the carbon fibres, and we find that an epoxy resin matrix, possibly with added polysulphone, is quite effective.

FIG. I is a perspective view of a blade of the present invention, the metal wire being shown in broken lines and the carbon fibres being shown in a broken away portion of the blade.

FIG. 2 is a chordwise section of the blade of FIG. 1.

FIG. 3 is a chordwise section similar to the view of FIG. 2 but showing a modified arrangement of the wire reinforcements.

FIG. 4 is a longitudinal sectional view of a further modification of the present invention.

FIG. 1 of the accompanying drawings shows how the piano wires may be distributed over a blade. The blade comprises an aerofoil section 10 and a root portion 11; it will be seen that the piano wires 12 are concentrated near the outer surface of the blade mainly and may also be near the leading and trailing edges of the aerofoil section, and that they extend from within the root section to end some three-fourths of the way up the zero- This would provide additional anchoring for the wire.

The principal of underlying the use of the steel wire reinforcement is summarised as follows: Because the carbon fibres (shown at 14 in FIG. 1) are linearly elastic to failure, large deformations, e.g., during impact, result in fibre fracture. Metal wires 12 are not linearly elastic to failure because plastic yielding can occur. Thus under impact it should be possible to retain a large degree of residual strengths in the blade, because of the presence of the unbroken metal wires.

The volume fraction of the wires that can be used must be kept to a minimum in the blade to keep the density to a minimum particularly since the square root of the Modulus/Density ratio determines the blade frequency; this must be as high as possible and since the impact loading is in bending this may be achieved by using the wires in the outer layers. (By using the configuration shown and steel wires of modulus 30 X l0p.s.i. compared with carbon fibres of slightly lower modulus the frequency of the blade is changed very little.) However, the volume fraction of wires must be sufficient to contain the GP. load on the blade after the carbon fibre fracture; this is about 10 percent.

- Steel wires are used because they have a similar modulus to the carbon fibres and therefore carry their equal share of the load and because they can be obtained at a low cost with strengths over 400 X10 p.s.i.

In testing examples of the construction proposed we have found that the piano wire reinforcement as well as providing a high residual strength gives a surprising improvement in the impact strength of a composite. Thus test pieces were made up by laminating sheets of carbon fibres made by the pyrolysis of polyacrylonitrile and pre-impregnated with an epoxy resin and latent hardener. Control test pieces were made with'the carbon fibre and epoxy resin alone; test pices for the blade construction of the invention were made by evenly dispersing some 10 percent by volume of piano wire of 5 X 10" inch diameter among the carbon fibres (whose diameter was 0.3 X lO inch) and the resin matrix.

1. Sample Manufacture Samples were made by lathe winding 5 X 10 inch diameter steel wires onto layers of carbon fibre epoxy foil. In this way the wires 12 are rigidly attached at the root, and extend over that portion of the blade most likely to be damaged by bird ingestion and to break off.

The outer one-fourth of the aerofoil is unlikely to break warp sheet on a steel former. When a sufficient number of layers were formed the carbon fibre epoxy/steel composite was compacted by pressing on the former at 500 lb/in at 160 C. Carbon fibre epoxy control standards were produced irithesame way.

Two series of tests were carriedout to simulate the effect of impact on a spinning blade.

a. Three point bend to constant deflection b. Longitudinal impact, i.e. fibres running along the specimen length, with impact at To measure the residual strengths in each test most of the samples were subsequently pulledin tension. 7 2 Typical Test Results y I 3Point Flexure Flexural Sample Residual Residual Stren Flexural Tensile X1 .s.i. Strength Strength X l0p.s.i. X l0p.s.i.

Carbon/ 2 03 I 24 18.3 Epoxy $11.6 i8 :18 Carbon, I v Epoxy 252 66 53.] Steel wires (about 10% Limits refer to 90 percent confidence limits.

The residual strength is based on the load supported by the beam after a fixed deflection.

Impact (Small Hounsfield,)

ing the large increase in residual strengths hoped for, the steel wire reinforcement 12 produces a substantial increase in flexural and impact properties. More efficient use of the steel reinforcement 12 could undoubtedly be made by selective reinforcement, e.g., near to the surface of the blade as discussed and with the wires only going part way up the blade length. As shown in FIG. 2, the wires 12 may be concentrated near the blade surface, the wires 12 preferably extending from the root 11 along a portion of the blade 10. In FIG. 3 there is disclosed a slightly different arrangement. of wires 12 and as will be noted, the wires 12 in this environment are concentrated near the leading edge and trailing edge respectively of the blade 10.

It was expected that when the carbon fibres fractured, the piano wire would be capable of plastically deforming to absorb energy and consequently would not break, forming a structure which would retain the blade together when it was subject to bird strike or the like. However, the above tests show that in addition to this behaviour which did appear in the broken test pieces, the piano wire reinforcement 12 also effecting a remarkable improvement in the basic properties of the material before fracture.

It will be appreciated that there are a number of ways of incorporating the piano wires into the composite. Thus one could introduce the wires into sheets of fibres to form pre-pregs, or complete sheets of the wires could be made and laid up with the carbon fibre sheets.

I claim:

1. A blade or vane for a gas turbine engine comprising a matrix material, a reinforcement of carbon fibres having a predetermined modulus of elasticity, said reinforcement of carbon fibres being embedded in the matrix material, and a further reinforcement of strong ductile metal wires with a modulus of elasticity similar to the predetermined modulus of elasticity of the carbon fibres, said metal'wires being embedded within the matrix and extending longitudinal of the blade.

2. A blade or vane for a gas turbine engine as claimed in claim 1 and in which the wire reinforcement comprises 10 percent by volume of the blade.

3. A blade or vane as claimed in claim 1 and in which said wires are concentrated near the blade surface.

4. A blade or vane as claimed in claim 1 and in which said wires extend from the blade root over only the major part of the longitudinal extent of the blade.

5. A blade or vane as claimed in claim 1 and in which said blade comprises an aerofoil portion and a root portion and in which wires extend down at least part of the blade, loop at the root portion of the blade, and extend back up at least part of the blade. I

6. A blade or vane as claimed in claim 1 and in which said wires are concentrated near the leading and trailing edges of the blade. I

7. A blade or vane as claimed in claim 1 and in which said matrix material comprises a major proportion of epoxy resin. 7

8. A blade or vane as claimed in claim 7 and in which said matrix material comprises an added proportion of polysulphone.

9. A blade or vane as claimed in claim 7 and in which said wire reinforcement comprises steel wires.

10. A blade or vane as claimed in claim 8 and in which said steel wires comprise piano wire.

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2. A blade or vane for a gas turbine engine as claimed in claim 1 and in which the wire reinforcement comprises 10 percent by volume of the blade.
 3. A blade or vane as claimed in claim 1 and in which said wires are concentrated near the blade surface.
 4. A blade or vane as claimed in claim 1 and in which said wires extend from the blade root over only the major part of the longitudinal extent of the blade.
 5. A blade or vane as claimed in claim 1 and in which said blade comprises an aerofoil portion and a root portion and in which wires extend down at least part of the blade, loop at the root portion of the blade, and extend back up at least part of the blade.
 6. A blade or vane as claimed in claim 1 and in which said wires are concentrated near the leading and trailing edges of the blade.
 7. A blade or vane as claimed in claim 1 and in which said matrix material comprises a major proportion of epoxy resin.
 8. A blade or vane as claimed in claim 7 and in which said matrix material comPrises an added proportion of polysulphone.
 9. A blade or vane as claimed in claim 7 and in which said wire reinforcement comprises steel wires.
 10. A blade or vane as claimed in claim 8 and in which said steel wires comprise piano wire. 